Liver fibrogenesis is a complex wound-healing process elicited by various chronic toxic stimuli. Hepatocyte apoptosis is a main feature of chronic inflammation in the liver, and recently we have demonstrated a direct link between hepatocyte apoptosis and fibrogenic activity in the liver. At the center of liver fibrogenesis are the hepatic stellate cells, which by phagocytosing apoptotic bodies of hepatocytes induce fibrogenic signaling pathways and production of extracellular matrix. Activation of the NADPH oxidase (NOX) is a crucial step in the induction of the fibrogenic activity following phagocytosis. Thus, our HYPOTHESIS is that NOX2 activation with superoxide production in HSC is a key event during liver fibrogenesis. To address this hypothesis our SPECIFIC AIMS will be to study the following areas where NOX2 activation may play a key role: 1. NOX2 increases HSC phagocytic activity of HSC 2. Phagocytosis and NOX2 activation induce fibrogenic signaling pathways 3. Phagocytosis and NOX2 activation induce liver fibrogenesis in vivo. The data emanating from this proposal will help define the mechanistic links between hepatocyte apoptosis resulting from chronic liver injury, phagocytosis and NOX2 activation in HSC, and the resulting oxidative damage and fibrogenic response. Furthermore, the proposed studies will yield important data on the early activation of HSC during fibrogenesis which may translate into designing rational therapeutic approaches to prevent progression of fibrosis.